Oven having multiple horizontal flow chambers

ABSTRACT

Oven for dough products, comprising an oven chamber having conveyance means for according to a vertical conveyance path conveying multiple trays with dough products through the oven chamber, and a number of horizontally positioned flow chambers placed one above the other at least one side of the conveyance path, wherein the flow chambers are adapted for in horizontal direction supplying heated air and deflecting the air to the oven chamber for evenly distributing the supplied air over a tray.

BACKGROUND OF THE INVENTION

The invention relates to an oven, particularly to an oven for food products, such as dough products.

In the food industry, particularly bakeries and other enterprises producing dough products, use is made of either large, elongated ovens in which the dough containing products are baked, often storey-wise, while being conveyed from an entrance to an exit, or smaller ovens, in which the products are treated stationary. Such ovens comprise a heating area with supporting means for baking trays, wherein heated air from the outside is passed into the heating area in order to circulate along the dough products. The heated air then arrives between the baking trays in a slightly uncontrolled manner, certain zones above the baking trays becoming hotter than others do. In case of for instance baguettes this may lead to bake-off differences over their length. A part of the hot air circulates outside of the baking trays, as a result of which this part only discharges heat to the walls of the heating area. Ovens are known of which the air circulation can be turned by means of (reversing) valves in the air ducts. Such valves however are sensitive to failures.

EP-A-1.520.473 shows an oven with a conveyance system for intermittent vertical conveyance of baking product carriers through the oven chamber. On either side of the conveyance path blow openings and suction openings are provided: In vertical direction blow openings alternate with suction openings, in horizontal direction per carrier position a blow opening and a suction opening. As a result the carriers in consecutive carrier positions are always provided with heated air from the opposite side. The, as considered in vertical direction, opposite air flows have an adverse effect on each other, resulting in baking differences in the flow direction. This is particularly disadvantageous in case of long bakery product carriers. Moreover a part of the air blown out will immediately be sucked away by the suction opening situated above and underneath and therefore not be passed over the bakery products.

It is an object of the present invention to provide an oven in which heated air can be effectively passed towards the dough products to be baked.

It is an object of the invention to provide an oven in which heated air can be evenly passed over dough products.

SUMMARY OF THE INVENTION

The invention, according to a first aspect, provides an oven for dough products, comprising an oven chamber having conveyance means for according to a vertical conveyance path conveying multiple trays with dough products through the oven chamber, and a number of horizontally positioned flow chambers placed one above the other at least one side of the conveyance path, wherein the flow chambers are adapted for in horizontal direction supplying heated air and deflecting the air to the oven chamber for evenly distributing the supplied air over a tray.

The trays for the dough products, such as baking trays, will usually be placed one above the other. The flow chambers can supply the heated air in this horizontal direction and distribute over a tray due to the deflection over a short distance.

Preferably the flow chambers have a flow-through profile of which the size decreases in supply direction. The deflection of the air supplied in horizontal direction can be enhanced due to this decrease, because the air flow in horizontal supply direction is subjected to an ever increasing resistance.

The path of the deflected air can be kept short particularly when the flow chambers are adapted for directing the supplied air transverse to the horizontal supply direction.

Preferably the flow chambers extend along a side of the conveyance path of the trays, so that the heated air can be supplied horizontally over this side and be distributed evenly.

In one embodiment the flow direction over immediately consecutive trays is substantially directed in the same direction. The air flows are then capable of reaching far over the trays which is particularly advantageous when large trays with a large number of dough products are used.

When the oven comprises a heating unit having air heating means and positioned adjacent to the conveyance path, wherein the flow chambers extend from the heating unit into the oven chamber, heating up the oven can remain limited to heating up the air heating means and the flow chambers. The other parts of the oven, particularly the walls of the oven chamber, can remain at a lower temperature, as a result of which the energy for the heating of the dough products can be efficiently used and baking differences due to local radiant heat can be counteracted.

The oven's capacity can be increased when the oven comprises multiple adjacently positioned groups of support means, wherein the flow chambers are positioned for generating a substantially closed air circulation per group of support means. Due to the substantially closed air circulations a certain air temperature can moreover be maintained independently per group, or the necessary capacity for heating the air can be set per group.

The distribution of the heated air over dough products on several trays carried one above the other, can be enhanced when the oven comprises air supply means for supplying heated air to the flow chambers that are positioned one above the other, wherein the air supply means are adapted for evenly distributing the heated air over the flow chambers.

In a first development the flow chambers are bounded by horizontally extending air injectors having a series of air outlets, preferably joined together, for discharging the supplied air.

The heated air can be deflected directly into the direction of the dough products when the air outlets are directed for discharging the supplied air to a tray.

It can be counteracted here that the heated air only reaches certain areas of the dough products, as a result of which these areas may get burnt due to over-heating, when the air outlets are directed for discharging the supplied air between the trays, wherein the conveyance means preferably are adapted for periodically pausing the conveyance of the vertically conveyed trays, wherein the pausing position of the trays is adapted to the position of the air outlets for discharging the supplied air between the trays. Preferably the air outlets are directed for bringing the supplied air towards or between the trays with a vertical, preferably upward or downward vertical directional component, so that in the supplied air turbulence may arise as a result of which several sides of the dough products can be evenly provided with heated air.

In one embodiment the oven comprises a series of air injectors at the same side of the conveyance path that are consecutive in vertical direction.

The heated air from the air injectors can be passed in the same direction over several consecutive trays when the immediately consecutive air injectors within the series of air injectors, preferably all air injectors within the series of air injectors, are destined for simultaneous discharge of supplied air.

In one embodiment the immediately consecutive air injectors within the series of air injectors, preferably all air injectors within the series of air injectors, over their longitudinal direction, considered at least within the ultimate ends of the series of air outlets, are separated from each other, particularly spaced apart from each other. The separation may enhance the discharge of heat from the injectors outside of the series of air outlets, as a result of which the air injectors are able to cool down properly after use. Furthermore the separation may make an adjustment of the air injectors possible.

Alternatively formulated, the immediately consecutive air injectors within the series of air injectors, preferably all air injectors within the series of air injectors, considered at least within the ultimate ends of the series of air outlets, at their longitudinal sides are free from a mutual connection.

The air injectors may each form a fixed unit when they are defined by a shape-retaining, preferably metal housing in which the series of air outlets are provided.

In a second, further development the oven comprises adjustment means for adjusting the outflow direction of the series of air outlets.

Preferably the adjustment means are adapted for adjusting the outflow direction of the air outlets in vertical direction, so that for instance the degree of the said turbulence in the heated air can be adjusted for an optimal baking result per type of dough product.

In a simple embodiment the air injectors are rotatable about a horizontal axis for adjusting the outflow direction of the air outlets in a vertical plane.

The degree of distribution of the supplied air over a tray with several dough products can be adjusted when the adjustment means are adapted for adjusting the outflow direction of the air outlets in horizontal direction and/or with a directional component in a longitudinal direction of the air outlets. In that way an even distribution of the supplied air over the tray can be achieved.

The outflow from the air injectors can be accurately directed when the adjustment means comprise one or more directing fins at the location of the air outlets, wherein the directing fins preferably can be adjustably swivelled with respect to the air outlets, preferably in horizontal and/or vertical direction.

The outflow can be directed, in several directions, over a large length of the air injectors when the adjustment means comprise several directing fins that are distributed over the series of air outlets, wherein the fins can be adjustably swivelled one to the other.

In a third, further development the oven comprises adjustment means for adjusting an outflow volume of the series of air outlets. Preferably the adjustment means are adapted for adjusting the outflow volume so as to be variable over the series. Optional pressure differences or pressure lowerings over the horizontal length of the injectors can thus be compensated for achieving an evenly distributed outflow. In that way the air flow can also be concentrated to those parts where dough products are actually present. This is for instance the case with adjacently spaced apart baguettes.

The outflow volume can easily be adjusted when the adjustment means comprise at least one movable visor at the location of the air outlets, wherein the visor preferably comprises an air slit. The air slit may enhance a turbulent outflow, as a result of which the dough products are provided with a turbulent air flow.

The outflow volume can be adjusted over the length of the air outlet when the adjustment means comprise several visors distributed over the series of air outlets.

Preferably the air injector comprises an elongated tube member that extends substantially free from the conveyance path into the oven chamber, wherein a wall of the tube member comprises at least one air outlet, wherein the wall of the tube member preferably is situated substantially free from the wall members of the oven that bound the oven chamber. Undesirable heat transfer from the air injectors to the walls of the oven chamber can thus remain limited.

In a fourth further development a number of horizontal flow chambers in opposite direction are part of an air circuit having a driven air propeller, wherein the air propeller preferably comprises an axial ventilating fan having a drive shaft. Said flow chambers that work in reverse are able to generate an even vacuum in the oven chamber, as a result of which the air also remains correctly distributed over the dough products during the further course.

Preferably the oven comprises two flow chambers on either side of the conveyance path, wherein the two flow chambers are situated in the same horizontal plane and are part of the air circuit. Due to the horizontal position one to the other a substantially horizontal air flow can be enhanced between two trays.

Preferably a direction of the air circuit is defined by a drive direction of the air propeller, preferably a drive direction of the drive shaft. Failure prone reversing valves for turning the air flow may thus be superfluous.

During a heating process of dough products the direction of the air flow can be turned several times when the oven comprises control means for periodically changing the drive direction of the air propeller, wherein the control means preferably comprise adjustment means for adjusting the period of the control means.

According to a further aspect the invention further provides an oven for dough products, comprising an oven chamber having conveyance means for according to a vertical conveyance path conveying multiple trays with dough products through the oven chamber, and air heating means that are adapted for generating an air circuit through the oven chamber by means of a driven air propeller, wherein the air propeller preferably comprises an axial ventilating fan having a drive shaft, wherein the direction of the air circuit is defined by a drive direction of the air propeller, preferably a drive direction of the drive shaft. Failure prone reversing valves for the air flow can thus be avoided.

According to a further aspect the invention further provides a method for heating dough products in an oven, wherein the oven comprises an oven chamber having conveyance means for according to a vertical conveyance path conveying multiple trays with dough products through the oven chamber, wherein the conveyance means are provided with support means for carrying the trays spaced apart one above the other, wherein the method comprises passing the support means through the oven in a fixed passage time, and according to a wanted capacity placing the trays with dough products selectively on the support means.

Due to the fixed passage time (adjusted once), the heating time for each introduced dough product is always the same, whereas the capacity of the oven can be varied indeed. Due to this method the capacity need not be varied by constantly changing a passage speed of the support means, which is highly complex as the overall heating time of the dough products per tray is then hard to keep up with.

The aspects and measures described and/or shown in the application may where possible also be used individually. Said individual aspects, such as the reversibility of air passed along the food products by turning the direction of rotation of the propeller or ventilating fan, the method of easily maintaining the heating time, and other aspects may be the subject of divisional patent applications relating thereto.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be elucidated on the basis of a number of exemplary embodiments shown in the attached drawings, in which:

FIG. 1 shows a side view in cross-section of a baking oven according to the invention;

FIG. 2 shows a top view in cross-section of the baking oven according to the line II-II in FIG. 1;

FIGS. 3A and 3B show side views, partially in cross-section, of the baking oven according to the lines IIIA-IIIA and IIIB-IIIB, respectively, in FIG. 1;

FIGS. 4A and 4B show side views, in cross-section, of the first oven column of the baking oven according to the lines IVA-IVA and IVB-IVB, respectively, in FIG. 2;

FIGS. 4C and 4D show top views cross-section of the first oven column of the baking oven according to the lines IVC-IVC and IVD-IVD, respectively, in FIG. 4B;

FIG. 5 shows a top view of air injectors and the position with respect to the baking trays in the first oven column;

FIG. 6 shows a side view, partially in cross-section, of the air injectors and the baking tray according to line VI-VI in FIG. 5, within the framework of VI in FIG. 4A;

FIG. 7 shows a front view of one of the air injectors according to FIGS. 5 and 6, considered from the baking tray; and

FIG. 8 shows a side view in cross-section of the air injector according to line VIII-VIII in FIG. 7, in which one of the fins of the air injectors is shown.

DETAILED DESCRIPTION OF THE DRAWINGS

The baking oven 1 as shown in FIG. 1 comprises a metal housing 2 provided with thermal insulation and having four oven columns 20, 70, 80, 90 placed therein one behind the other for the warming or heating of, in this example, baguettes 11 that are positioned transversely on the elongated baking trays 10.

The baking oven 1 comprises four vertical passage conveyors 21, 71, 81, 91 for vertical conveyance of the baking trays 10 through the oven columns 20, 70, 80, 90, a horizontal supply conveyor 4 for supplying baking trays 10 to the first oven column 20 through an entrance opening 12 in the housing 2, two horizontal passage conveyors 27, 67, situated above and a passage conveyor 57 situated below for passing the baking trays 10 between the consecutive vertical passage conveyors 21, 71, 81, 91, and a discharge conveyor 5 for discharging the baking trays from the last oven column 90 through a discharge opening 17 in the housing 2.

The vertical passage conveyors 21, 71, 81, 91, as shown in detail in FIG. 4A near the passage conveyor 21 of the first oven column 20, have each been built with two pairs of opposite metal pillar guides 23, having horizontal shafts 22 at their ends with chain wheels along which endless chains 26 are guided. The chains 26 are mutually connected per pair to horizontally situated support or angular profiles 24, wherein the distance between two angular profiles 24 that are placed straight opposite each other is such that with their lower sides they engage below a baking tray 10 and keep it in the engaged condition with the upright sides. The circulating movements of the chains 26 are synchronised, as a result of which the carried baking trays 10 are always held horizontally.

The horizontal conveyors 4, 57, 5 situated below have been built with endless chains that are not further shown on which the baking trays 10 may lie. The horizontal passage conveyors 27, 67 situated above have been built with endless chains that are not further shown having flights for at the end of the vertical conveyors 20, 80 sliding the baking trays 10 through in horizontal direction to the angular profiles 24 of the next vertical conveyor 71, 91.

When operational the baking trays 10 are passed in horizontal direction A into the baking oven 1 and subsequently passed upwards in direction B through the first oven column 20 by the first vertical passage conveyor 21. After transfer by the first horizontal passage conveyor 27 in horizontal direction C the baking trays are passed downward in direction D through the second oven column 70. Said path is repeated in the next oven column 80, 90 in the same directions F, G, H, after which the baking trays 10 are passed out of the baking oven in direction J.

As shown in FIG. 2 a hot air installation 25, 75, 85, 95 is positioned in the housing 2 adjacent to each oven column 20, 70, 80, 90. The oven columns and the hot air installations are further described below on the basis of the first oven column 20 and the first hot air installation 25 according to FIGS. 3A-4D.

As shown in FIGS. 3A-4D the first hot air installation 25 comprises a heating case 29 that is made of sheet metal. At the inside the heating case 29 is subdivided into a first vertical air distribution channel 30 having horizontal passage tubes 31, and vertical air heating channel 32 which via an opening 35 at the upper side is connected to the first air distribution channel 30, and a second vertical air distribution channel 33 having horizontal passage tubes 34 which via an opening 36 at the bottom side is connected to air heating channel 32. The passage tubes 31, 34 have a round cross-section and are regularly spaced apart, considered in horizontal direction each time per pair opposite each other at the same level. The passage tubes 31, 34 extend parallel to each other from the heating case 29, in the direction of the oven column 20.

The first hot air installation 25 further comprises two gas hearths 37 that discharge heat to a heat exchanger having pipes 38 that extend through the air heating channel 32. At the upper side of the air heating channel 32 an electrically driven horizontal propeller or ventilating fan 28 is placed, of which the direction of rotation can be changed. The propeller 28 is designed like an axial ventilating fan or axial propeller, wherein the air flow is turned in axial direction from the central shaft or drive shaft by reversing the direction of rotation of the drive shaft. At the upper side and the lower side of the air heating channel 32 air humidifiers 48 are accommodated.

As shown in FIG. 3B the first air distribution channel 30 is subdivided by means of vertical partitions 61 and inclined partitions 62 into nine deflecting sub channels 63, and which for each passage tube 31 form an individual connection to the opening 35 at the upper side of the air heating channel 32. As shown in FIG. 3A the second air distribution channel 33 is also subdivided by means of vertical partitions 65 and inclined partitions 66 into nine deflecting sub channels 68, wherein the sub channels 68 form an individual connection for the passage channels 34 to the opening 36 at the lower side of the air heating channel 32.

The passage tubes 31, 34 at the heating case 29 form attachment points for tubular air injectors 200 which from the air distribution channels 30, 33 extend in horizontal direction along the vertical conveyors 21 in the oven column 20. The air injectors 200 are shown in detail in FIGS. 5-8. As shown in FIGS. 5 and 6 the injectors 200 extend over the full length of the baking trays 10, and they are spaced apart from the baking trays 10 at a short distance from the long edges of the baking trays 10. In vertical direction the further discussed outer walls of the consecutive air injectors 200 are spaced apart from each other. The longitudinal sides of the air injectors 200 have no mutual contact or direct connection.

The air injectors 200 comprises an attachment tube 201 having a circular cross-section that fits over the circular passage tubes 31, 34, an outlet part 204 having a rectangular cross-section, and a transitional part 202 for transition from the round attachment tube 201 to the rectangular outlet part 204. The outlet part 204 has an upper wall 210 and a lower wall 212 that are parallel to each other, a first rear wall section 203 parallel to the centre line R of the attachment tube 201, a second rear wall section 211 declining inclined to the centre line towards the end 250 of the outlet part 204, and a longitudinal outlet opening 207 (FIG. 7) parallel to the longitudinal sides 13 of the baking tray 10. At the upper side and the lower side the outlet opening 207 is bounded by turned lips 213 at the upper wall 210 and the lower wall 212 which lips are parallel to each other. The outlet opening 207 extends over substantially the full longitudinal side 13 of the baking trays 10.

At the upper side and the lower side of the outlet opening 207 air dosage plates 214 are attached over the lips 213, which air dosage plates 214 are slidably adjustable in direction W (FIG. 8) transverse to the outlet opening 207. Parallel to the lips 213 attachments strips 216 are attached over the air dosage plates 214 which attachment strips partially cover the air dosage plates 214. The attachment strips 216 are secured to the lips 213 by means of bolts 215, wherein the bolts 215 extend through long holes 221 in the air dosage plates 214, as a result of which they are only slidable within the length of the long holes 221 between an open position as shown in FIG. 7 at the left-hand side of the outlet opening 207, and a closed position as shown at the right-hand side of the outlet opening 207.

The air dosage plates 214 are provided with air slits 241 that can partially be covered by the attachment strips 216, or by sliding the plates 214 can be slid over the outlet opening 207 for locally limiting yet not fully closing off the air flow at the location of the plates 214.

Between the air dosage plates 214 the air injectors 200 comprise vertical metal fins 230 that are attached to turned attachment lips 217 at the attachment strips 216 by means of threaded ends 218 and nuts 219. The fins 230 can swivel in horizontal direction U for directing the air flow. The fins 231 have a bevelling 231 in order to be able to place the air injectors 200 in an inclined position as close to the baking trays 10 as possible when this is necessary.

Due to the circular cross-sections of the passage tubes 31, 34 and the attachment tubes 201, the air injectors 200 can be fully adjusted so as to swivel about the centre line R in the direction T as shown in FIGS. 5 and 6, as a result of which the outflow direction of the outlet opening 207 can be directed with respect to the baking trays 10 that pass by the air injectors 200. The attachment tubes 201 have been provided for that purpose with long holes 206 (FIG. 7) transverse to the centre line R of the attachment tubes, through which screws 40 have been secured in the air passage tubes 31, 34. When the oven is only used for one specific bakery product, the adjustable ability to swivel is superfluous. In that case the air injectors are fixedly connected to the heating case 29 for instance by means of welding. According to need another position can be used per vertical passage conveyor 21, 71, 81, 91.

When the baking oven 1 is operational, an air circulation is kept going in the oven column 20 due to the action of the propeller 28. The air is then sucked away horizontally in direction M (FIG. 3A) by the air injectors 200 at the first air distribution channel 30 and deflected via the sub channels 63, after which the air is driven vertically upwards in direction Q and subsequently driven through the opening 35 past the propeller 28. Subsequently the air flows in vertical direction P (FIG. 4B) downward along the pipes 38 of the heat exchanger of the activated hearths 37 to be heated (again), after which the air is passed upwards via opening 36 in direction N (FIG. 3A) through the sub channels 68 of the second air distribution channel 33. The air is then evenly distributed over the sub channels 68. After deflecting in the sub channels 68 in direction K, the air is passed in horizontal direction in the air injectors 200 at the second air distribution channel 33. Due to the adjustment of the air dosage plates 214 and the decreasing cross-section of the air injectors in flow direction K, the air is deflected and proportionally driven over the length of the baking trays 10 in direction L (FIG. 6) over and between the baking trays, wherein the direction L of the flow is directed by the fins 230. The flow L can be turbulent, as a result of which the baguettes are provided all round with hot air.

As shown in FIG. 6 the air injectors 200 are directed such in direction T that the hot air is driven in the flow direction L upwards between the baking trays 10, as a result of which the baguettes 11 are only indirectly provided with hot air. Due to the vacuum as formed by the air injectors 200 at the first air distribution channel 32, the introduced air is passed back again to the heating case 29 to be heated again. Passing heated air over the baguettes 11 is enhanced because all air injectors 200 at the same side of the vertical passage conveyor 21 discharge heated air in the direction of the baking trays 10.

The direction of rotation of the propeller 28 is periodically turned, for instance every two minutes, by turning the direction of rotation of the drive shaft, as a result of which the air flow L over the baguettes is reversed and the baguettes 11 are evenly baked on both sides. The passage time per vertical passage conveyor 21, 71, 81, 91 is approximately six minutes, as a result of which the baguettes 11 per vertical course are subjected to at least one change in air flow direction L.

Per oven column 20, 70, 80, 90 a more or less closed air flow is generated, as a result of which the hot air flows of the oven columns hardly influence each other. Additionally a partitioning wall of thermal insulating material can be placed between the oven columns 20, 70, 80, 90. The first two hot air installations 25, 75 each have two hearths for a quick heating up of the baguettes 11 that are introduced cold, the third and fourth hot air installation 85, 95 each have only one hearth to maintain the heat in the baguettes 11.

The baking trays 10 in this example have a width of approximately 800 mm and a length of approximately 1600 mm. The size of the baking trays 10 can be varied, wherein for instance a length of approximately 2000 or 3000 mm is used. Due to this increase for instance more baguettes 11 placed parallel and adjacent to each other fit on a baking tray. The length of the air injectors 200 then needs to be adjusted accordingly, so that the bakery products are provided with heated air over the full length of the baking tray in the manner described above. 

1-37. (canceled)
 38. Oven for dough products, comprising an oven chamber having a conveyor for according to a vertical conveyance path conveying multiple trays with dough products through the oven chamber, and a number of horizontally extending air injectors having a series of air outlets and bounding horizontally positioned flow chambers, wherein at one side of the conveyance path the air injectors are arranged in a first series of air injectors that are consecutive in vertical direction, and, with respect to the conveyance path at one side opposite of the first series, in a second series of air injectors that are consecutive in vertical direction, wherein the air injectors with the flow chambers are adapted for in horizontal direction supplying heated air and deflecting the air to the oven chamber via the series of air outlets for evenly distributing the supplied air over a tray, wherein the immediately consecutive air injectors within the first series are destined for simultaneous discharge of supplied air and the air injectors in the second series in opposite direction and together with the injectors of the first series are part of an air circuit having a driven air propeller, wherein the oven comprises a control for periodically changing the drive direction of the air propeller during vertical conveyance of the trays.
 39. Oven according to claim 38, wherein the opposite air injectors of the first and second series are situated in the same horizontal plane.
 40. Oven according to claim 38, wherein all immediately consecutive air injectors within the first series of air injectors are destined for simultaneous discharge of supplied air.
 41. Oven according to claim 38, wherein a direction of the air circuit is defined by a drive direction of the air propeller.
 42. Oven according to claim 38, wherein the air propeller comprises an axial ventilating fan having a drive shaft.
 43. Oven according to claim 42, wherein a direction of the air circuit is defined by a drive direction of the drive shaft.
 44. Oven according to claim 38, wherein the control comprises an adjustment for adjusting the period of the control.
 45. Oven according to claim 38, wherein the series of air outlets is joined together.
 46. Oven according to claim 38, wherein the flow chambers have a flow-through profile of which the size decreases in supply direction.
 47. Oven according to claim 38, wherein the flow chambers are adapted for directing the supplied air transverse to the horizontal supply direction.
 48. Oven according to claim 38, wherein the flow direction over immediately consecutive trays is substantially directed in the same direction.
 49. Oven according to claim 38, comprising a heating unit having an air heater and positioned adjacent to the conveyance path, wherein the flow chambers extend from the heating unit into the oven chamber.
 50. Oven according to claim 38, wherein the conveyor is adapted for according to several consecutive vertical conveyance paths conveying the trays through the oven chamber, wherein the flow chambers are positioned for generating a substantially closed air circulation per conveyance path.
 51. Oven according to claim 38, wherein the immediately consecutive air injectors within the series of air injectors, over their longitudinal direction, considered at least within the ultimate ends of the series of air outlets, are separated from each other.
 52. Oven according to claim 38, wherein the immediately consecutive air injectors within the series of air injectors, considered at least within the ultimate ends of the series of air outlets, at their longitudinal sides are free from a mutual connection.
 53. Oven according to claim 38, wherein the air injectors are defined by a shape-retaining metal housing in which the series of air outlets are provided.
 54. Oven according to claim 38, wherein the series of air outlets extends in longitudinal direction of the air injectors and parallel to a side of a tray.
 55. Oven according to claim 38, wherein the air outlets are directed for discharging the supplied air between the trays, wherein the conveyor is adapted for periodically pausing the conveyance of the vertically conveyed trays, wherein the pausing position of the trays is adjusted to the position of the air outlets for discharging the supplied air between the trays.
 56. Oven according to claim 38, wherein the air outlets are directed for bringing the supplied air to or between the trays with an upward or downward vertical directional component.
 57. Oven according to claim 38, wherein the air injectors comprise an elongated tube member that extends substantially free from the conveyance path into the oven chamber, wherein a wall of the tube member comprises at least one air outlet. 